class Solution {
public:
    int hIndex(vector<int>& citations) {
        int n = citations.size(), left = 0, right = n - 1;
        while (left <= right)
        {
            int mid = left + (right - left) / 2;
            if (citations[mid] >= n - mid)
            {
                right = mid - 1;
            }
            else
            {
                left = mid + 1;
            }
        }
        return n - left;
    }
};